The present invention relates to a process for checking the operability and effectiveness of a catalyst for purification of the exhaust gases of a combustion engine. The process is particularly suitable for monitoring a diesel oxidation catalyst. The operability of the catalyst is monitored according to the invention by measuring the conversion of carbon monoxide in combination with a temperature measurement. The process is also suitable for monitoring the operability of catalysts for the HC-DeNOX process and the urea-SCR process and for NOX adsorber catalysts,.
For motor vehicles with a gasoline engine it is obligatory to monitor the functioning of all the exhaust gas-relevant components of the exhaust gas system during operation of the vehicle by an on-board diagnosis system (OBD system). Malfunctions of one or more components of the exhaust gas system are indicated by a warning lamp lighting up. In the case of vehicles fitted with a catalytic converter for after-treatment of the exhaust gases, the operability of the converter must also be monitored by the OBD system.
In the future it will be necessary for diesel motor vehicles also to be fitted with an OBD system. In addition to recycling of the exhaust gases and the exhaust system, the OBD system will also include monitoring of diesel particulate filters, and in particular of diesel oxidation catalysts. In the case of vehicles with gasoline engines, an indirect OBD process is employed for monitoring three-way catalysts, in which the oxygen storage capacity of the catalyst is measured and evaluated. This process cannot be used on diesel engines, sine these are always operated with excess oxygen, that is to say with a lean air/fuel mixture.
An object of the present invention is therefore to provide a process for checking the operability of an exhaust gas purification catalyst which is also suitable for checking the functioning of oxidation catalysts for diesel engines and allows determination of the catalyst activity directly via measurement of the conversion of carbon monoxide (CO).
The above and other objects of the present invention can be achieved by a process described herein which is characterized by fining a combustion engine with an electronic control system comprising engine electronics and OBD electronics, and evaluating the remaining catalytic activity of the catalyst by determining the difference xcex94T between the current catalyst exit temperature of the exhaust gas TE and the start-up temperature for carbon monoxide TCO,50%, fresh of the fresh catalyst or new catalyst at the particular operating point of the engine by the equation
xcex94T=TExe2x88x92TCO,50%, fresh
and evaluating the degree of conversion for rCO carbon monoxide.
In the context of this invention the light-off temperature for carbon monoxide oxidation is understood as meaning that temperature TCO,50% at which carbon monoxide is just converted to the extent of 50%.
According to the invention the catalytic activity still remaining after a certain operating time is evaluated directly. Characteristic parameters for this are the degree of conversion rCO for carbon monoxide, the current catalyst exit temperature of the exhaust gases TE and the light-off temperature of the fresh catalyst for CO, TCO,50%,fresh, which is a function of the engine speed and the load and can be pre-stored in the OBD electronics.
The degree of conversion rCO for carbon monoxide can be determined according to the following relationship                                           r            CO                    =                      1            -                                          c                                  CO                  ,                  2                                                            c                                  CO                  ⁢                  .1                                                                    ,                            (        2        )            
wherein cCO,2 is the concentration of carbon monoxide in the exhaust gas measured downstream of the catalyst and cCO,1 is the concentration of carbon monoxide in the exhaust gas measured upstream of the catalyst.
Alternatively, there is the possibility of determining the degree of conversion rCO for carbon monoxide according to the following relationship                                           r            CO                    =                      1            -                                          c                                  CO                  ,                  2                                                            c                                  CO                  ,                  engine                                                                    ,                            (        3        )            
wherein CCO,2 is the concentration of carbon monoxide in the exhaust gas measured downstream of the catalyst and CCO,engine is the carbon monoxide concentration at the current engine operating point stored as an engine map in the OBD electronics.
In both cases the carbon monoxide concentrations can be measured with the aid of carbon monoxide sensors.